The present invention relates to biodegradable plastics. More specifically, the present invention relates to biodegradable plastics having an enhanced rate of biodegradability resulting from the presence of compressed powdered plant fiber such as, for example, fine fiber from coconut mesocarp. In particular, the present invention relates to an improvement in biodegradable plastics wherein the biodegradability is made predictable by blending conventional polymers, biodegradable polymers and biodegradability enhancing compressed plant fine fiber powder having moisture expansion characteristics capable of generating structure disrupting internal mechanical forces upon prolonged exposure to the environment. In other words, the present invention relates to plastics which decompose in the soil after use.
Because of environmental issues facing society, environmentally degradable plastics are increasing in popularity. The biodegradable plastics currently developed are divisible into four categories that somewhat overlap: a) the natural polymers which use polysaccharides such as starch and the like; b) the microbial polyesters which use the biological activity of microorganisms; c) blends with accelerated degradation properties which are regular plastics with degradation accelerator additives; and d) chemical synthetics which include the aliphatic polyesters and the like.
Depending on the particular properties of the different materials, biodegradable plastics are used as raw materials for disposable products and in products that generally do not have to carry heavy loads. Such applications include: agricultural products such as films, sheets, bottles, pots, and bags; products for daily use and tableware such as trays, cases, and straws; some medical equipment; and sports equipment. Nonetheless, the use of biodegradable plastics is still limited and their effect on the general plastics industry as a whole is limited.
A review of the "state of the art" for environmentally degradable polymers is found in: "Encyclopedia of Chemical Technology" 4th edition, Vol. 19, Pages 968-1004, John Wiley & Sons Inc. (1996), the entirety of which is incorporated herein by reference. Additionally, a review of manufacturing processes and testing procedures in current use, in: "Encyclopedia of Chemical Technology" 4th edition, Vol. 19, Pages 290-347, John Wiley & Sons Inc. (1996), is incorporated herein, in its entirety, by reference.
Biodegradable plastic offers promise to solve the problem of the disposal of regular plastic. But there have been several obstacles. Depending on the type and ratios of the components in the biodegradable plastic and depending on the environment where the biodegradable plastic is disposed, the rate of biodegradation may be less than desired. Another obstacle is that as the thickness of the product containing biodegradable plastic increases, the biodegradability property is diminished. Furthermore, the life span of the product containing biodegradable plastic might be detrimentally shortened as a result of insects causing damage. A greater problem still is that many polymers are specifically formulated to serve narrow optimized functions, or to display certain manufacturing process behaviors. Substitution with a biodegradable plastic diminishes the effectiveness of these processes and generates an inferior final product. It would therefore be highly advantageous to formulate a way to improve the biodegradability of all plastics while maintaining each plastic's desirable features.
One possibility for achieving this goal would be through the use of an additive to the plastic, in place of currently used common fillers, that increases the plastic's susceptibility to environmental degradation. Additives to plastics are currently used to obtain desirable properties in the plastic. For example, additives are used to impart such properties as strength, hardness, flexibility, color, etc. An extensive review of properties, applications, and toxicologies of additives for plastics is found in: "Chemical Additives for the Plastics Industry", prepared by Radian Corp., Noyes Data Corp, N.J. (1987), the entirety of which is incorporated herein by reference. One possibility of a plastic additive to increase environmental degradability may be a biomaterial such as plant fiber or wood powder.
Palms, particularly coconut palms, bear fruit and are widely cultivated in the tropics. The palms have been traditionally used in various ways. Referring to FIG. 2A, a view of a coconut 2, taken in longitudinal section, shows an endosperm 2c which has a typical thickness of 10 to 20 mm and is generally used for coconut oil, food, or as raw material for medicines. A hard, woody endocarp 2b, commonly known as the shell, typically has a thickness of 2 to 6 mm. The coconut shell is useful for making a good quality industrial grade of activated carbon. A mesocarp 2a, commonly called the husk, forms the largest part of the coconut fruit, with a typical thickness of 30 to 40 mm. However, the fibers within the mesocarp are used currently only to make string and rope and are not generally used for anything else.
Referring to FIG. 2B, a coconut fiber 3, from mesocarp 2a is seen in a radial cross-section. Coconut fiber 3 is classified botanically as a sclerenchymatous fiber. Typically, coconut fiber 3 is approximately 0.7 mm long and 20 micrometers wide. Structurally, the fiber includes an inner membrane 3a, saw tooth projections 3b, and a hollow pit 3c. Physically, coconut fiber 3 is light, hard, and resilient. Thermally, coconut fiber 3 is a poor conductor of heat. Furthermore, coconut fiber 3 is durable against water and air (Shoichiro Nagai, Inorganic and Organic Industrial Material Handbook p. 788, (S35, 3, 20) 1st edition, published by Toyo Keizai Shinposha, the entirety of which is herein incorporated by reference).
After being compressed, coconut fiber 3 also has the characteristic that its volume increases by 5 to 6 times when water is added. This phenomenon is hypothesized to be a result of the compressed dried fibers having original shape memory, with inner membrane 3a returning to its maintenance state at the cellular level. It is therefore postulated that the expandability characteristics of this and other plant fibers may impart a useful enhancement to plastic biodegradation processes.
Referring now to FIG. 2C, coconut fiber 3 has a dense growth of beard-like fine fibers 31 around a trunk 32. Fine fibers 31 drop off from trunk 32 under normal conditions when normal coconut fibers 3 are collected and manufactured into, for example, rope. Fine fibers 31 are often themselves collected and used to improve cultivating soil in Europe.
Fine fibers 31 contain a large amount of hemicellulose, which attracts microorganisms. Trunk 32, in contrast, contains large amounts of phenolic lignin, which acts to repel microorganisms. Under normal conditions, unprocessed coconut fibers 3 would not attract microorganisms, due to the presence of phenolic lignin in coconut trunk 32. Therefore, the use of unprocessed coconut fibers 3 does not enhance biodegradation of plastics incorporating such fibers.